Cognitive Multi-User Free Space Optical Communication Testbed

Multi-point free space optical communication (FSOC) has been identified as a valuable and promising technology for meeting high-capacity and -density demands of future space and terrestrial communication networks. FSOC's point-to-point nature has boosted extensive research on technologies and methods that support multi-user optical networks. An FSOC system platform is essential for fully characterizing, testing, and evaluating state-of-the-art, multi-user prototypes and technologies developed by both businesses and academic communities. This paper presents an experimental FSOC testbed that demonstrates next generation FSO systems and allows cognitive, multi-point communication. These systems provide a significant improvement over those with currently hampered with single-user limitations. The FSOC testbed is multi-node, modular, and high-speed with real-time ability to test O-PHY modules and O-MAC schemes. The testbed consists of multiple, independently tunable optical transmitters and receivers that can be configured to emulate various communication scenarios (e.g., point-to-point (P2P), point-to-multipoint (P2MP), and multi-point-to-multipoint (MP2MP). At the receiver side, a cognitive controller performs real time, blind processing of received signals for identifying the number of concurrent transmissions. Accordingly, the controller drives an optical switch to route detected signals to pre-defined paths. Given that a single-user transmission is detected on multiple paths, diversity combining will be performed to improve received signal-to-noise ratio (SNR). If multiple-user transmissions are identified, signals are routed into separate high-speed photodetectors for processing. The work described below details hardware components integrated in the platform, as well as software development for the cognitive controller. Furthermore, this work provides an experimental demonstration of the testbed capabilities for single-user and multiple-user scenarios.